For the apostle John, the idea that a Christian will continually or habitually practice sin goes against everything that John intends.
John's reference to "antichrists", meant that they were evident in the church in his lifetime. It is not a 20th or 21st century arrival.
A Christ like walk is attained, based on the maturity level of the believer.
Man, is not perfect, nor will he be perfect on this earth. There is nothing that man can do that will make him good enough to walk in the light. However, John makes it very clear that Christians are “walking in the light”, not due to anything if they have accomplished, rather, it is what Jesus accomplished on the cross.